The present invention relates to a television camera apparatus or an image pickup apparatus and more particularly to a depth-of-field control apparatus and image pickup apparatus having the same therein for obtaining an image which is of great depth of field and is of high resolution.
In a television camera apparatus utilizing an image pickup tube, or a solid-state imaging device and a camera lens, the best focal length is obtained by adjusting a focus ring of a lens. At this time, a range in a direction of depth allowing an image to be taken or shot with a resolution substantially equal to that of the best focal length, i.e., a depth of field is determined by a lens aperture. More specifically, in a state in which the aperture of the lens is increased, the depth of field is shallow. In other words, the range allowing an image having a focal length near the best focal length to be obtained becomes narrow. Conversely, in a state in which the aperture of the lens is decreased, the depth of field becomes greater so that the range allowing a sharp image to be obtained is increased.
In a high definition television system which is anticipated as the next generation-television system, system design has been performed mainly for the purpose of providing an image of high resolution. It is also required for a television camera apparatus used for the high definition television system to have a high resolution property. In the meantime, since an image signal of high resolution is processed in the high definition television system, the band width of a signal processing circuit is about 30 MHz which is about 6 times as large as that of 4 to 6 MHz in the current television system. Accordingly, the noise band width is widened, and therefore, the power of noise mixed therein is increased. Then, the quantity of light made incident on the image pickup device is increased for the purpose of improving the signal to noise ratio (SNR). In the normal shooting in a studio or the like, the quantity of light for illumination is increased to realize the increase in the quantity of incident light. On the other hand, in the case where the quantity of light cannot be changed as in outdoor shooting, the aperture is increased to cope with such. Accordingly, in this case, the depth of field becomes shallow, so that the range allowing a sharp image to be obtained will be necessarily limited.
In the field of a microscope, a still-camera and the like, there has been well known a technique in which images located in a plurality of different focal lengths are composed to obtain a wide depth of field. For example, such a technique is disclosed in Takatoshi Ota et al: "A Method for Image Composition Using Image Variance", National Conference Record of the Institute of Electronics and Communication Engineer's of Japan, Vol. J66-D, No. Oct. 10, 1983, Satoshi A. Sugimoto et al: "Digital Composition of Images with Increased Depth of Focus Considering Depth Information", APPLIED OPTICS, Vol. 24, No. 14, Jul. 15, 1985, and the JP-A-1-309478. (Incidentally, JP-A-2-212809 (laid open on Aug. 24, 1990) which has not yet been yet laid open at the priority date of the present application also relates to the control of the depth of field).